I try to find as level a spot as possible but haven't worried about perfectly level, within reason. I try to get the head of the bed on the high end. Harbor Freight sells a cheap inclinometer that is a quick check on the counter and fits in the kitchen drawer.
We have one fridge that is 15 years old and one that is 19 years old and the only problems we have had was once when a controller board went out and once when the vent fan died(it's mounted in the slide).
With our TC and vehicle, fridge is mounted on a side wall, I calculated, we could be up to 10 inches side to side and 13 inches front to rear. That's using the Mfgr. specs.
I don't think we've ever been out of level more than half that for an overnight.
